Synthesis and investigation of mono- and binuclear cyano-bridged complexes of rhodium,ruthenium, and palladium

Binuclear Rh^III and Ru^II complexes of the [M¹-CN-M²]⁺BF ₄ ^– (M¹ and/or M² are (⁵-Cp)(³-C₃H₅)Rh and (⁶-C₆H₆)(³-C₃H₅)Ru) type, heteronuclear organometallic compound (⁵-Cp)(³-C₃H₅)RhCNPd(³-C₃H₅)Cl, and mononuclear Rh^III and Ru^II complexes [(³-C₃H₅)LM(MeCN)]⁺ _BF4 ^– (M = Rh, L = ⁵-Cp; M = Ru, L = ⁶-C₆H₆) were synthesized. An electrochemical study of these compounds in solutions demonstrates that the bond between the bridged CN ligand and the metal atoms is rather strong, and there is no dissociation into mononuclear fragments in solutions. The kinetics of the reaction of [(⁵-Cp)(³-C₃H₅)Rh(MeCN)]⁺ _BF4 ^– with halide ions was studied by electrochemical methods. The ligand exchange proceeds by a bimolecular dissociative-exchange mechanism.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 968–973, May, 1995.     

Thermal decomposition of cobalt nitrato compounds: Preparation of anhydrous cobalt(II)nitrate and its characterisation by Infrared and Raman spectra

The thermal decomposition of Co(NO₃)₂·6H₂O (1) as well as that one of NO[Co(NO₃)₃] (Co(NO₃)₂·N₂O₄) (2) was followed by thermogravimetric (TG) measurements, X-ray recording and Raman and IR spectra. The stepwise decomposition reactions of 1 and 2 leading to anhydrous cobalt(II)nitrate (3) were established. In N₂ atmosphere, cobalt oxides are finally formed whereas in H₂/N₂ (10% H₂) cobalt metal is produced. Rapid heating of cobalt(II)nitrate hexahydrate causes melting (formation of a hydrate melt) and therefore side reactions in the hydrate melt by incoupled reactions and evolution/evaporation of different species as, e.g., HNO₃, NO₂, etc. In case of larger amounts in dense packing in the sample container, the formation of oxo(hydoxo)nitrates is possible at higher temperature. For 2, its thermal decomposition to 3 was followed and its decomposition mechanism is proposed.     

Theoretical Study of Rotational Isomerism in Ethyl Pseudohalides

The structure and conformational stability of ethyl pseudohalides CH₃CH₂ — XCN (X = O, S, Se) were investigated using ab initiocalculations at the MP2 level of theory with a triple- basis set augmented with polarization and diffusion functions. Full optimization was performed on the minimum energy structures as well as on the transition state forms. The relative stabilities of rotational conformers were calculated at the MP4 level using MP2 optimized reference geometries. The nature of all considered stationary points was verified by calculation of the harmonic vibrational frequencies. The calculated bond lengths, bond angles, dipole moments, and rotational constants of optimized global minima structures agree very well with the corresponding experimental data obtained from microwave spectroscopic studies. Also, available experimental frequencies are in good accord with the theoretical values. For ethyl cyanate CH₃CH₂ — OCN, the antiperiplanar (trans) form is predicted to be more stable than the synclinal (gauche) form, and the synperiplanar (cis) form corresponds to the transition state. For both ethyl thiocyanate CH₃CH₂ — SCN and ethyl selenocyanate CH₃CH₂ — SeCN, the gaucheform is the global minimum while the trans-conformer is a local minimum and the cis-form is a transition state.     

Charge control in the formation of complexes of phenol with ethylene derivatives containing organoelemental group IVB substituants

The v(OH) frequency shifts of phenol and the v_R resonance components of these shifts in the IR spectra of phenol H-complexes with ethylene derivatives containing various substituents including organosilicon, organogermanium, and organotin groups have been studied. The relationship between v and v_R and the values that characterize the influence of substituents on the effective charges of the double bonded carbon atoms was established; the latter values have been calculated previously usingab initio quantum chemical methods. The effective charges for the compounds with organoelemental substituents have been calculated. It has been elucidated that of the two types of possible interactions, charge controlled and orbital controlled, occurring in the formation of a complex of a hard acid, phenol, with the studied ethylene derivatives, the former is predominant.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1383–1387, August, 1993.     

The reactions of 2-benzoylpyridine with [RuHCl(CO)(PPh3)3] and [(C6H6)RuCl2]2

The reactions of [RuHCl(CO)(PPh₃)₃] and [(C₆H₆)RuCl₂]₂ with 2-benzoylpyridine have been examined, and two novel ruthenium(II) complexes – [RuCl(CO)(PPh₃)₂(C₅H₄NCOO)] and [RuCl₂(C₁₂H₉NO)₂] – have been obtained. The compounds have been studied by IR and UV–Vis spectroscopy, and X-ray crystallography. The molecular orbital diagrams of the complexes have been calculated with the density functional theory (DFT) method. The spin-allowed singlet–singlet electronic transitions of the compounds have been calculated with the time-dependent DFT method, and the UV–Vis spectra of the compounds have been discussed on this basis.     

Conformation of poly(L-glutamic acid) in aqueous solutions of linear amphiphiles with a cationic group at both ends

The conformations of poly(l-glutamic acid) [P(Glu)] in solutions of the bipolar amphiphile 1,20-icosanediylbis(alkylammonium chloride) [C20(RA)₂], where RA includes trimethylammonium (TMA), dimethylammonium (DMA), or methylammonium (MA), were investigated with measurements of the circular dichroism spectra at 10–35 °C. All C20(RA)₂ induced an α-helix of P(Glu) in the aqueous solutions. The residue molar ellipticity at 222 nm showed a similar dependence on the amphiphile concentration (C _s) below 0.5 of the ratio of 2C _s to the residue concentration (C _p) of P(Glu), but it separated into three directions at 2C _s/C _p>0.5. C20(MA)₂ induced an α-helix of P(Glu) at 2C _s/C _p<0.5 followed by a helix aggregate at 2C _s/C _p>0.5. C20(DMA)₂ and C20(TMA)₂ also induced an α-helix, but a helix aggregate. C20(TMA)₂ indicated a strong temperature dependence and did not induce a complete α-helix at 35 °C. Received: 20 June 2001 Accepted: 6 September 2001     

Investigation of the Curing Mechanism in the GPTS/APTS Binder System

The acid catalyzed sol-gel reaction in the mixed binder system, 3-glycidoxypropyltrimethoxysilane (GPTS)/3-aminopropyltriethoxysilane (APTS) was investigated and one step and two step synthesis process were compared. Hydrolysis product was observed using the ¹H, ¹³C NMR and Raman spectra. Especially, based on the Raman spectra, epoxy ring opening was observed, varying the ratio of GPTS to APTS. The two step process made clear sol, while the one step process resulted in a milky suspension. According to the Raman spectra, the epoxy ring opening reaction kinetics proceeded slower in the two step process than one step process. Throughout the two step process, it was possible to apply the binder for the coating of substrate.     

Spectroscopic and Quantum Mechanical Studies of Substituted Anilines and their Charge-Transfer Complexes with Iodine in Different Solvents

Summary. Equilibrium constants and molar extinction coefficients for 1:1 charge-transfer complexes between 2-hydroxyaniline (HA), 5-chloro-2-hydroxyaniline (CHA), and 4-bromo-2,6-dimethylaniline (BMA) as donors and iodine, as a typical σ-acceptor were determined spectrophotometrically in chloroform, dichloromethane, and carbontetrachloride solutions. Spectral characteristics and formation constants are discussed in terms of donor molecular structure and solvent polarity. The stoichiometry of the complexes was established to be 1:1. For this purpose, optical data were subjected to the form of the Rose-Drago equation for 1:1 equilibria. Electronic absorption spectra of the studied anilines were measured in different solvents. Spectral data were reported and band maxima were assigned to the appropriate molecular orbital transitions (π–π^* and n–π^* electronic transition). Solvent effects on the electronic transitions were discussed. Optimized geometry of the studied anilines was obtained at B3LYP/6-31 + G(d). The effect of the electronic factors of the substituents on the geometrical parameters of the ring has been explored. Geometrical values of the ring deviate from the regular hexagonal ring. Intramolecular H-bonds in HA and CHA have been computed at B3LYP/6-31 + G(d) and MP2/6-31 + G(d) levels. The H-bonding distance was calculated to be 2.105 ? in HA and 2.127 ? in CHA. Abstracted from her M.Sc. thesis     

Acid–Base Equilibrium and Self-Association in Relation to High Antitumor Activity of Selected Unsymmetrical Bisacridines Established by Extensive Chemometric Analysis

Unsymmetrical bisacridines (UAs) represent a novel class of anticancer agents previously synthesized by our group. Our recent studies have demonstrated their high antitumor potential against multiple cancer cell lines and human tumor xenografts in nude mice. At the cellular level, these compounds affected 3D cancer spheroid growth and their cellular uptake was selectively modulated by quantum dots. UAs were shown to undergo metabolic transformations in vitro and in tumor cells. However, the physicochemical properties of UAs, which could possibly affect their interactions with molecular targets, remain unknown. Therefore, we selected four highly active UAs for the assessment of physicochemical parameters under various pH conditions. We determined the compounds’ pK_a dissociation constants as well as their potential to self-associate. Both parameters were determined by detailed and complex chemometric analysis of UV-Vis spectra supported by nuclear magnetic resonance (NMR) spectroscopy. The obtained results indicate that general molecular properties of UAs in aqueous media, including their protonation state, self-association ratio, and solubility, are strongly pH-dependent, particularly in the physiological pH range of 6 to 8. In conclusion, we describe the detailed physicochemical characteristics of UAs, which might contribute to their selectivity towards tumour cells as opposed to their effect on normal cells.     

Mathematical Models for Unstable Quantum Systems and Gamow States

We review some results in the theory of non-relativistic quantum unstable systems. We account for the most important definitions of quantum resonances that we identify with unstable quantum systems. Then, we recall the properties and construction of Gamow states as vectors in some extensions of Hilbert spaces, called Rigged Hilbert Spaces. Gamow states account for the purely exponential decaying part of a resonance; the experimental exponential decay for long periods of time physically characterizes a resonance. We briefly discuss one of the most usual models for resonances: the Friedrichs model. Using an algebraic formalism for states and observables, we show that Gamow states cannot be pure states or mixtures from a standard view point. We discuss some additional properties of Gamow states, such as the possibility of obtaining mean values of certain observables on Gamow states. A modification of the time evolution law for the linear space spanned by Gamow shows that some non-commuting observables on this space become commuting for large values of time. We apply Gamow states for a possible explanation of the Loschmidt echo.